Organoiodine complexes: a structural and functional

1772

Russian Chemical Bulletin, International Edition, Vol. 58, No. 9, pp. 1772—1784, September, 2009

Organoiodine complexes: a structural and functional variety M. S. Chernovýants and I. V. Burykin Southern Federal University, 7 ul. Zorge, 344090 RostovonDon, Russian Federation. Email: [email protected] The present review summarizes the results of structural studies of organoiodine complexes. Particular emphasis is given to the role of intermolecular interactions such as halogen— halogen (I...I), hydrophobic, π—π stacking, and hydrogen bonds (C—H...I) in the formation of supramolecular iodinecontaining architectures. The molecular formula, size, shape, and stability of the polyhalide ion and the way of its coordination by an outersphere cation or an organic macromolecule depend on the nature and symmetry of the cationic environment, the ability of a solvating solvent to form complexes with iodine, and the conditions of the synthesis. Efforts have been made to highlight a structural and functional variety of iodinecontaining complexes and estimate the prospects of using them as organic conductors, magnetic materials, liquid electrolytes, and biologically active compounds. Key words: iodine halides of organic cations, UV spectroscopy, NMR spectroscopy, Xray diffraction analysis, estimation of the stability constants, disproportionation kinetics, ab initio quantum chemical calculations, polyiodides.

The wide spectrum of action and high therapeutic effect of iodinecontaining drugs, as well as the use of molecular iodine preparations as disinfectants and anti septics, stimulate physicochemical investigations of io dine complexes with the aim of predicting their pharma cological and bactericidal properties. A promising area of application of iodine complexes is production of conducting polymers and organic semi conductors, liquid electrolytes, polymer carriers, and anionexchange resins.1,2 Iodine is known3 to be used as a radioactive label (ion 125I3–) for the study of the structures and activities of biologically active compounds (also for their quantification). Iodinecontaining com posites with polyvinylpyrrolidone (iodovidon), polyvinyl alcohol (iodinol), and a nonionic surfactant (iodonat)4 are prodrugs that can transform in vivo virtually com pletely into a biologically active form functioning like molecular iodine but with a weak irritating effect on tissues. Examples of anionic complexes with molecular iodine are the iodine halides CtXI2 (Ct is an organic cation; X = Cl, Br, or I). This approach is employed in the design of drugs combining the biological activities of an organic constituent and molecular iodine. Design of active iodine drugs containing an iodine complex with a quaternary ammonium salt on a polymer substrate holds promise.5 The invention of conducting conjugated polymers doped with molecular iodine6,7 won the 2000 Nobel Prize in chemistry.

A search for unique properties that would allow vari ous iodine complexes to find new areas of application stimulates both the targeted synthesis of organic iodine halides and their comprehensive experimental and theo retical study (including quantum chemical calculations and Xray diffraction analysis). Estimation of the biologi cal activity and other properties that directly depend on the form in which iodine exists in solutions and in the crystalline state is impossible without studying the struc tural features and stabilities of iodinecontaining drugs.8,9 The use of iodinecontaining systems as antimicrobial agents and drugs, as well as the high activity of molecular iodine and its compounds, stimulates a wide spectrum of investigations into the kinetics, thermodynamics, and structural analysis.10,11 The present review mainly covers the following types of iodine complexes: outersphere complexes D•I2 formed by donor—acceptor interactions of iodine with organic bases (D); iodine halides of organic cations CtXI2 (Ct+ is an organic cation; XI2– (X = Cl, Br, or I) are iodine containing complex anions bound by the threecenter molecular orbital);12,13 and polyiodine iodides of organic cations CtI–2n+1 (n = 2—4) with the iodide or triiodide ion as a complexing agent and molecular iodine as a ligand.14 Molecular adducts of elemental iodine Interest in the study of iodine compounds is due not only to commercial needs but also to an exceptional role

Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1716—1728, September, 2009. 10665285/09/58091772 © 2009 Springer Science+Business Media, Inc.

Organoiodine complexes

of iodine in biochemistry because its electrondonating and withdrawing properties allow the formation of com plexes with many organic compounds. The unique elec tronic properties of the iodine molecule, a peculiar “mo lecular probe”, are used to examine the structural features and thermodynamics of molecules.15,16 Recent investiga tions show substantially increased interest in the study of reactions of iodine with biomolecules. On the one hand, this is motivated by searching for a correlation between the characteristics of donoracceptor complexes and the physiological activity of their constituent molecules; on the other hand, this is due to development of a number of biologically active compounds and drugs based on molecular iodine complexes.17 Some studies are devoted to the mechanism of com plexation between molecular iodine and oxygencontain ing organic compounds (including solvents) and to esti mation of the stabilities of the resulting complexes. In the monograph,18 great attention is given to the electronic absorption spectra, geometries, and stabilities of charge transfer complexes of iodine with organic compounds and solvents. Interactions of cluster fragments of solvents ((Solv) n, Lewis bases) with molecular iodine (Lewis acids) have been considered. 19 The influence of the nature of the solvent and the number of its molecules in a cluster on the complexation thermodynamics has been studied. The formation of structures (Solv)n•I2 occurs by intermolecular donor—acceptor interactions of the electronegative sites of the solvent with iodine atoms. This is accompanied by charge transfer between the frag ments I2 and (Solv)n and the polarization and lengthening of the bond in the iodine molecule.20,21 A considerable number of studies are devoted to reac tions of halogen molecules as electron acceptors with organic donors. The latter include σdonors such as alkylamines, nitrogen heterocycles, nitriles, alcohols, esters, carbonyl compounds, sulfides, selenides, and organophosphorus compounds and πdonors (mostly, arenes and some heterocycles).22—30 Crystals of the stable organic metal β(ET)2(IBr2)0.7(I3)0.3 (ET is the cation of bis(ethylenedithio)tetrathiafulvalene) have been obtained by chemical oxidation of bis(ethylenedithio)tetrathia fulvalene with IBr in nitrobenzene.31 The IR and Raman spectra of highconductivity organic composites prepared by solidstate complexation between bis(ethylenedioxy) tetrathiafulvalenes and molecular iodine have been examined for the first time.32 A large body of experimental (Xray diffraction and Raman spectroscopic) data have been reviewed33 to ex plain the bonding nature in polyiodides and molecular adducts of the type donor—I2 and to find a correlation between Xray diffraction data and Raman spectra. At tention has been given to possible misinterpretation of the form of triiodide species as the symmetric ion I3– or the

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 9, September, 2009 1773

adduct I–•I2 from Raman spectra because of the instab ility of test samples under analytical conditions. A large body of literature data on the structures of molecular (including iodine) complexes and the thermo dynamics of their formation have been analyzed in the review.34 A clear correlation has been found between the enthalpy of formation of the complex (–ΔH) and the characteristic parameter Δr = rDA – a1(rD + rA),

where rDA is the donor—acceptor bond length determined using microwave spectroscopy and Xray diffraction; rD and rA are the tabulated values of the homeopolar cova lent radii of the heteroatoms linked by this bond; the empirical coefficient a1 is 0.901±0.007. As complexes become stronger, the donor—acceptor bond length approximates to the sum of the heteropolar covalent radii of the corresponding atoms and Δr tends to zero. For Δr >> 1, the components of complexes are held together by weak van der Waals interactions. A threestep mechanism of a reaction of iodine with organic bases (electron donors, D) has been proposed from spectrophotometric data. According to the mecha nism, the outersphere complex D...I—I forms rapidly and then transforms more slowly into the innersphere complex [D—I]+I–, which finally reacts with molecular iodine to give [D—I]+(I3–).12 Organic iodine halides In recent years, considerable attention has been given to the synthesis, structural characteristics, and thermody namic stability of iodine halides of nitrogencontaining organic cations.19,35—37 A recent review35 covers investiga tions into the chemistry of polyiodides from 1970 till 2002 and shows a vast structural variety of solid and liquid polyiodides with unique properties regarding electron conduction. The basic properties of iodine halides depend on the degree of interaction between three species as main building blocks: I–, I2, and I3–. A DFTcalculated (in the threecenter approximation with four electrons for the MO of I3–) fragment of the energy diagram for the molecular orbitals of I2 and I3– is shown in Fig. 1. About 900 triiodides with symmetric and asymmetric triiodide ions have been structurally characterized,38 the asymmetry of the ion being attributed to hydrogen bond ing (the shortest H...I contact is ~2.5 Å) and interionic interactions. The formation of anions containing more than one iodine molecule is attributed to interactions between the components of main building blocks. The higher polyiodide ions show higher bond anisotropy and are structurally more complex than the ion I3–. The results of theoretical and experimental studies on the

1774

Russ.Chem.Bull., Int.Ed., Vol. 58, No. 9, September, 2009

Fig. 1. Fragment of the diagram of interactions of the molecular orbitals for the anion I3– (see Ref. 35).

chemistry of polyiodine iodides (iodine complexes con taining five and more iodine atoms in the anion) have been summarized in a review.14 It has been noted that polyiodine iodide anions containing five and more iodine atoms can not only be discrete (I5–, I7–, I9–, and I82–) but also form chains with triiodide and pentaiodide ions as structural units. 39—41 When the external conditions remain constant, the stability of the anions drops from I5– to I9–. The anion I5– is an angular species, which may be regarded as being formed by coordination of two iodine molecules to the iodide ion. The I—I bond lengths in I5– (2.82 and 3.17 Å) are close to those in the asymmetric triiodide ion (Fig. 2). A calculation37 of the energies of formation of the anion I5– in the reaction I– + 2 I2 = I5–

M. S. Chernovýants and I. V. Burykin

validates the formation of the thermodynamically favor able Vshaped configuration rather than linear, Lshaped, and Tshaped configurations. The pentaiodide ion in the form of a linear structural unit has been represented42 as a model of disordered or disproportionate structures. The heptaiodide ion can be formulated as [(I3–)•2I2], – [(I )•3I2], or [(I5–)•I2] with a more or less distorted pyramidal geometry or in the Zform. The crystal struc ture of (PPh4)I7 contains the heptaiodide [(I3–)•2I2].43 Although (Et)4NI7, (UrPr)I7, and (EtPh3P)I7 have the – same anion configuration [(I3 )•2I2], their structures differ.44 A reaction of the diazacrown ether N,Ndibenzyl 1,4,10,13tetraoxa7,16diazacyclooctadecane (DD18C6) with iodine in chloroform yields the chargetransfer com plex [DD18C6H 2]I 8 (see Ref. 45). The structure of the complex has been confirmed by UVVIS, IR, and Raman spectroscopy and Xray diffraction. Octaiodide of N,Ndiprotonated macrocycle is stabilized by three center hydrogen bonds N—H(...O)2 in the inner cavity of the macrocycle. The octaiodide anion consists of the central unit I2 (dI—I = 2.768 Å) connected to two asym metric anions I3– (dI—I = 2.813 and 3.064 Å) and exists in a nearly planar Zconfiguration. The structure of the nonaiodide [(I3–)•3I2] has been assigned to the anion in the complex [K(15Cr5)2]I9 (Cr is crown ether). Three iodine molecules are coordi nated by a slightly asymmetric triiodide ion through con tacts 3.40—3.50 Å long. In the crystal structure, the ions I9– are held together by weak secondary interactions and van der Waals contacts.46 The nonaiodide structure can be depicted as the pyramidal ion I7– bonded to an iodine molecule.47 Compounds with eleven iodine atoms in the anion (I11– and I113–) have been mentioned.48 Fragments of the polyiodide structures are shown in Fig. 2. The molecular, crystal, and electronic structures of (P)10(I3–)4(I2)10 (1) and [P´]3(I3–)3(I2)7 (2) (P and P´ are pyrene and 1,3,6,8tetrakis(methylthio)pyrene, respec tively) have been described.49 In both systems, the organic

Fig. 2. Fragments of polyiodide structures33 with bond lengths (Å) and angles (deg).



molecules form cationic stacks separated by a polyiodide network. Different intermolecular interactions in the crys tal structure 1 have been arranged in the order of decreas ing Gibbs energy: halogen—halogen (I...I), hydrophobic, π—π stacking, and hydrogen bonds (C—H...I). A correla tion between the length of the intermolecular CH...I con tact and the bond angle has been plotted using data from the Cambridge Structural Database (CSD).49 The angle for a strong hydrogen bond is near 180°, while weaker hydrogen bonds are characterized by much smaller angles (140°—160° for a bond length of 3.0 Å and 100°—130° for a bond length of 3.6 Å). A CSDbased distribution of the iodine—iodine bonds in organic polyiodides over the bond length is shown in Fig. 3.49 The distribution peaks appear at 2.88 (valence bonds in the molecule I2 and the anion I3–) and 3.96 Å (intermolecular contacts in polyiodides and complex polyiodide networks). Intermolecular inter actions in the crystal structures of organic polyiodides have been subjected to topological analysis; it has been emphasized that a certain (≤15%) proportion between the inorganic and total volumes of the atoms in a molecule should be observed for a compound to have supercon ducting properties. The electronic absorption spectra of solutions of com pounds with the anions I5–, I7–, and I9– are identical with those of triiodide ions (λmax = 295 (logε 4.65) and 365 nm (logε 4.40)).14 Compounds with hypervalent iodine in the anions I3– and I5– and the cation containing a quaternary N atom constitute a small group of salts; they are liquids at room temperature37,50 and are used as electrolytes.51,52 A study of a structure—properties—function correla tion in polyhalides of nitrogencontaining heterocyclic Number of structures 320

240

160

80

2.6

3.0

3.4

3.8

4.2 d/Å

Fig. 3. Joint contribution of the distances I—I and I...I (d) in organoiodine complexes according to the CSD data.49

cations is of particular interest because such compounds exhibit high biological activity. To obtain compounds capable of releasing molecular iodine, Ncetyl(decyl)pyridinium diiodine chloride (I2Cl–), diiodine bromide (I2Br–), and triiodide (I3–) have been isolated preparatively.53 According to Xray diffraction data for Ncetylpyridinium triiodide and iodine halides, organic polyhalides in the crystal are packed in regularly alternating layers of nitrogencontaining cations and iodine halide anions.54 No shortened intermolecular con tacts have been detected in the crystal structures. Unlike aliphatic quaternary ammonium iodides, both Ncetyl and Ndecylpyridinium iodides coordinate two iodine molecules in chloroform to give very stable pentaiodides (logβ1 = 4.94, logβ2 = 8.41 and logβ1 = 5.01, logβ2 = 8.57, respectively; data from UVVIS study).53 NSubstituted quinolines are widely employed as materials with secondorder nonlinear optical behavior; the properties of such materials directly depend on the composition and spatial arrangement of their molecules.55 A systematic series of quinolinium (1ethylquinolinium, 1ethyl2,4dimethylquinolinium, and 1,2,4trimethyl quinolinium) triiodides has been examined.37,56 These de rivatives differ in both melting points and the ability of retaining molecular iodine. Their molecular structures have been examined by Xray diffraction. The cationic and anionic layers in the crystal of lowmelting (m.p. 34 °C) 1ethylquinolinium salt alternate along the axis c; in the nearly centrosymmetric anion, the distances I—I are 2.915(2) Å and the angle I—I—I is 179.08(6)°. The anions I3– are united into long chains aligned with axis b through strongly shortened intermolecular contacts 3.805 and 4.184 Å long (the double van der Waals radius of the iodine atom is 4.29 Å)57 (Fig. 4). The anionic chain of 1ethyl2,4dimethylquinolinium triiodide (m.p. 102—103 °C) is made up of alternating shortened intermolecular contacts I...I (3.935(4) and 4.151(4) Å). In the crystal of 1,2,4trimethylquinolinium triiodide (m.p. 169—170 °C), two types of chains are built from anions linked by either shortened (3.808 Å) or longer intermolecular contacts I...I (3.964 Å). The bond lengths in the anions I3– are not equalized, ranging from 2.883 to 2.964 Å for 1ethyl2,4dimethylquinolinium salt and from 2.892 to 2.943 Å for 1,2,4trimethylquinolinium salt. The angles I—I—I approximate to 180°. Spectrophoto metric studies with the average iodine number function have revealed that iodides of the aforementioned cations coordinate different numbers of iodine molecules in chloroform: 1ethyl2,4dimethylquinolinium iodide forms very stable pentaiodide (logβ1 = 5.11, logβ2 = 8.6), while the other iodides exist as triiodides (logβ = 4.15 for 1,2,4trimethylquinolinium and logβ = 4.66 for 1ethyl quinolinium).56 Iodine molecules usually tend to unite into anionic polyiodine iodide chains [Ix]– when a counterion is planar

1776


a

z x y 0

I(3c)

I(1c)

I(2c)

b

I(3d)

I(2b)

I(1b)

I(1d) I(2d)

I(2a)I(1a)

I(3a)

I(3b)

Fig. 4. Fragment of the crystal structure [C9H7NC2H5]I3 along the axis x (a) and the fragment of the anionic chain (b) (see Ref. 37).

and can form a stacked structure with channels suited to the polyiodide chain in size and geometry. For instance, in tetrathiafulvalene polytriiodide, stacked cations with an interplanar spacing of 3.32 Å accommodate in their channels linear chains of interconnected symmetric ions I3– with an interionic distance of 3.00—3.64 Å.14 A series of the isostructural halogenated tetrathiafulvalenes (TTF)


(Br 2—EDT—TTF) 2IBr 2, (Br 2—EDT—TTF) 2I 3, and (I2—EDT—TTF)2I3 (EDT is ethylenedithio) have been obtained by condensation of 4,5dibromo or 4,5diiodo 1,3dithiole2thiones.58 In the crystalline state, these salts show directed interactions Hal...Hal both between or ganic molecules in adjacent stacks and between the halo gen atom of an organic molecule and the terminal atom of the anion. These salts are conducting (0.5—10 S cm–1) at room temperature and behave like semiconductors when cooled. The structural chemistry of 3,6bis(dimethylamino) acridine polyiodides has been studied.59 A product ob tained by a reaction of the base with iodine (1 : 2) in ethanol and dichloromethane has been formulated as [C17H19N3(H)]2(I)2•3I2 and that isolated from acetone, as [C17H19N3(H)]I5. It has been concluded28 that acridine and its derivatives can form various iodinerich complexes and salts. In addition, the stability and molecular and crystal structures of 9amino10methylacridinium tri iodide have been studied.60 According to Xray diffrac tion data, its structure consists of linear triiodide anions and 9amino10methylacridinium cations stacked via π—πinteractions (Fig. 5). The average bond length in the triiodide ion is 2.915 Å. Some difference in the I—I bond lengths (2.9097(6)—2.9206(6) Å) is due to unequal par ticipation of the iodine atoms in the Hbonds. Stacking in this structure reflects the specific nature of the organic cation; the ions I3– are bound to the cation by a system of hydrogen bonds with different strengths. The shortest I...H contacts involve the amino (2.99 Å) and methyl H atoms (3.15 Å). Organic dications that have not only triiodide but also an electronegative halide anion as counterions can serve as a basis for template synthesis of long 2D polyiodide chains and ribbons. New supramolecular architectures

b

a

0

Fig. 5. Fragment of the crystal structure [C14H13N2]+[I3]– (see Ref. 60).

c



Fig. 6. Twodimensional supramolecular architecture [AdeH22+](Cl–)(I3–)(H2O). Particular types of atoms are distinguished by blue (I), green (Cl), red (O), light blue (N), gray (C), and white colors (H) (see Ref. 61).

have been built from diprotonated adenine molecules and polyiodides [AdeH22+](X–)(I3–)(H2O) (X = Cl or Br).61 The cations AdeH22+ dimerize through NH...N hydrogen bonds. The dimers form 1D ribbons with X– bridges. Posi tively charged zigzag ribbons of nanometric width act as long hydrogenbonded templates, thus stimulating the for mation of zigzag polyiodide ribbons as twinned polyiodide chains. Oppositely charged ribbons form a 2D structure with alternating positive and negative bands ~1 nm wide which are complementary in shape, size, and charge (Fig. 6). Such structures can be of interest for the design of electric nanodevices such as electron or proton wires.62,63 Subtle structural changes in the crystalline state of compounds of the general formula R3PI4 have been examined by solidstate NMR spectroscopy and Xray diffraction studies (see Ref. 57). For R = Pri, the mono cation Pri3PI+ interacts with the terminal atoms of the anion I3– to form the cation [(Pri3PI)2I3]+ whose charge is compensated by the isolated ion I3–. For R = Pri2N, the resulting salt (Pri2N)3PI4 shows a very weak interionic interaction. Enhancement of the properties of drugs through the use of hydrophilic highmolecularweight compounds (HMWC) becomes a problem of current interest. Such composite materials contain additives that can control the release of the active ingredient from a drug and regu late its solubility. Drug—HMWC formulations are usually prepared with poly(ethylene oxides), poly(vinyl alcohol), polyvinylpyrrolidone, polyacrylamide, etc. as substrates.64 These compounds provide continuous supply of drugs into an organism so that their concentration is close to a minimum therapeutic level and does not reach a toxic level. The equilibrium distribution of various iodine forms (free iodine, triiodide, polymeric iodine triiodide and

triiodide complexes, and iodide ion) in aqueous solutions of povidone—iodine drugs has been analyzed.65 The choice of HMWC allows the concentration of free iodine to be maintained at a level of bactericidal effect (5 mg L–1). The presence of polyiodide chains in the structures de pends, to some degree, on the HMWC structure. For instance, polyiodide chains keep linear geometry in the presence of polymeric substrates. Thorough examination66 of the crystal structure of a guest—host complex of amy lose with iodine has revealed two amylose chains passing through the crystal cell. The conformation of either chain is a lefthanded helix stabilized by intramolecular hydro gen bonds. The cavity of the helix is occupied by a nearly linear chain of five iodine atoms spaced at 2.80 and 3.22 Å (obviously, in the form of pentaiodides). It has been experimentally proved67 that the formation of a complex of molecular iodine with amylose involves no iodide ion. According to spectrophotometric estimation, the sta bility constants of guest—host complexes are of the order of 102. These complexes can be regarded as models of active sites in complex biological objects.68,69 Organonitrogen, phosphorus, arsenic, and sulfur interhalides, their synthesis, and their investigations using optical spectroscopy and Xray diffraction are abundant in the world´s scientific literature. Interest in the theoreti cal study of such complexes is primarily due to the neces sity of finding structure—property correlations, as well as to their unusual structure (the presence of the inter halogen hypervalent bond Hal—I and the interionic bond Ct...HalI 2) and thermodynamic stability. 19,70,71 The structural variety29,30,49,72,73 and wide spectrum of proper ties exhibited by organic iodine halides and polyiodides (e.g., a high electron conductivity characteristic of liquid complexes at room temperature52,74 and biological activity)

1778


attract the attention of researchers. In the last few years, new reagents based on hypervalent iodine species have been introduced into the methodology of modern organic synthesis.75 Iodine compounds find use for redox76 and complexation reactions77 in analytical chemistry. Quantum chemical and spectrochemical studies of the stabilities of iodine halides of organic cations. The bonding in polyiodides, which are hypervalent compounds, is a subject of theoretical discussion (e.g., see Ref. 13). Re cently,13,70,71 it has been demonstrated that accurate description of interactions in halogencontaining organic systems imposes special requirements on the level of ab initio calculations. At present, calculations in pseudo potential basis sets are available and widely used for iodinecontaining systems.78 Correlation studies of the relative stabilities of mixed trihalides in the gas phase and in solutions are of primary importance.70,71,79 That is the reason why calculations that allow estimation of the influence of the solvating medium on the configuration and thermodynamic stability of both separate trihalide anions and those in organic interhalides become increas ingly frequent.79—82 Theoretical calculations of separate trihalides XI2– (X = Cl, Br, or I) with consideration to solvating media15,70,71 (performed in electrostatic and con tinual models) confirm the destabilization of the anions in polar solvents. Moreover, comparative analysis of these systems in the gas phase leads to the following order of decreasing relative stability (with respect to the decompo sition into X– and I2): ClI2– > BrI2– > I3–. This order is the reverse of that obtained experimentally in solutions.20,54 Thus, the presence of solvating (even lowpolarity) media considerably influences the formation of iodine halides and reverses the order characteristic of the gas phase. The formation of iodine halide anions in solutions has been represented19 as competitive interactions of iodine mol ecules with cluster fragments of solvents and a solvated halide ion. All calculations have been performed with the GAMESS program 83 in the combined basis set 631G++(d,p) for the H, C, N, O, and S atoms and in the basis set HW+(3d) for the I atom. According to the calculated data, molecular complexes of iodine with clus ter fragments of solvents ((Solv)n•I2) show the following order of the decreasing relative stability: Me2SO > MeOH > H2O > MeCN > CHCl3. These results correlate with the experimental stability constants determined earlier 84 from spectrophotometric data for molecular complexes of iodine with solvents. For dipolar aprotic solvents (MeCN and Me2SO), the stability of molecular iodine complexes is mainly controlled by the electrondonating ability of electronegative atoms; i.e., molecular complexes of I2 with Me2SO are the most stable ones (β = 3.38), while those with MeCN are least stable (β = 0.11). For lower aliphatic alcohols, the stability constants range from 0.34 to 0.55. The results obtained have been used in model structures of iodine halide anions with cluster fragments of solvents.36


It has been found that the formation of solvated iodine halide anions results from displacement of solvent clus ters from the solvation shells of the halide ion (X–) and I2. Thus, the anions Cl– and Br–, which are more strongly shielded on the side of solvents, tend less to form interhalide ions XI2–. Comparative quantum chemical analysis of solvated and separate interhalides CtXI2 shows that the solvation effects of molecular solvent clusters on the tendency of the anions to decompose into X– and I2 should be taken into account.19,36 Disproportionation kinetics of iodine halides in iodine coordinating solvents. In modern scientific literature, the mechanism of interconversions of iodine halides in iodinecoordinating solvents is under discussion. To implement targeted synthesis of interhalides of organic cations, such factors as the cation structure, the presence of an electronegative atom in the anion, and the solvent nature should be taken into account. Consideration of the solvation effect of iodine halides in the PCM context with all corrections has predicted full disproportionation of asymmetric anions in polar media, in contrast to the gen eralized Born model, which leads to the same stability order as for the gas phase: I2Cl– > I2Br– > I3–. The dispro portionation of iodine halides includes the following steps: cleavage of the bond Br(Cl)...I in the complex, the for mation of the molecular complex Solv•I2, and the trans formation of molecular iodine into the triiodide ion (see Ref. 18). I2X– + Solv I2•Solv

X– + I2•Solv [I–...I+]•Solv

[I–...I+]•Solv + I2X–

I3–...Solv + IX

According to Xray diffraction data, recrystalliza tion of Npropylisoquinolinium diiodine bromide gives crystals with different molecular formulas when chloro form is replaced by iodinecoordinating diethyl ether (C 12H 14Br 0.40I 2.60N) and iodineinert light petroleum (C12H14BrI2N).85 The form in which iodine exists in the compound influences the pharmacological and therapeutic proper ties of organic polyhalides and thus is crucial for their possible use as drugs. This necessitates elucidation of the mechanism and determination of the kinetic parameters of interconversions of different iodine forms in iodine coordinating solvents (or polymers) used in drug prepa ration. A number of recent studies20,85—87 have been devoted to the spectrophotometric analysis of the dispro portionation kinetics of organic diiodine bromides and diiodine chlorides of quaternary ammonium (cholinium, tetraalkylammonium, and Nsubstituted pyridinium and isoquinolinium) cations and quaternary phosphonium cations under the action of solvents. The spectral changes


observed in the system diiodine halide of an organic cat ion—iodinecoordinating solvent reflect the dispropor tionation of the anionic iodine molecule in a polar sol vent followed by the formation of the triiodide ion 2 CtXI2 + Solv = CtX(Solv) + CtI3(Solv) + XI(Solv).

In all cases, the processes under study are described by a firstorder reaction equation and the rate constants are calculated by the formula kt = ln[(Amax – A0)/(Amax – Ai)],

where A0, Ai, and Amax are the initial, current, and maxi mum optical densities at the peak wavelength of the re sulting triiodide ion. The values of the rate constants suggest a substantial influence of the solvent nature and the cation structure on the disproportionation rate of diiodine halides. The dis proportionation of acetylcholinium and carbacholin ium diiodine halides proceeds most slowly in methanol (k ≈ 3•10–4 min–1); the reaction is reversible in MeCN (k+ ≈ 1•10–4 min–1, k– ≈ 2•10–4 min–1). The dispropor tionation rate constants of tetraalkylammonium iodine halides in methanol are 4—5 times higher than those for cholinium derivatives. In MeCN, the rate constants are of the order of 2•10–4 min–1 and the reaction is irreversible. The rates of the irreversible disproportionation of iodine halides of nitrogencontaining heterocations (except for longchained cetylpyridinium) and quaternary phospho nium cations are higher by one order of magnitude than the disproportionation rate of tetraalkylammonium salts in alcohols and by nearly two orders of magnitude in MeCN. On the whole, the disproportionation rates of diiodine halides in alcohols are higher than those in MeCN, probably because of the formation of the transi tion state [R—OH2+...I–...I+...–O—R], which is known in aqueous solutions of iodine and is associated with autoprotolysis of an amphiprotic solvent. Structures and thermodynamic stability of iodine halides. The synthesis of polyiodide systems, their struc tures and bonding, and examination using optical and magnetic resonance methods (Raman, farIR, NQR, and Mössbauer spectroscopy), Xray diffraction, and conductometry have been reviewed.35 The structures of trialkylsulfonium triiodides35,88 and the crystal structures of poly(3alkylthiophenes) doped with elemental iodine89 have been characterized by Raman and farIR spectro scopy. To identify the products of iodine disproportion – – ation (anions I3 and I5 ) and the bonding nature in polyiodides, the latter structures have been subjected to Xray diffraction. A number of papers17,60,90—92 are concerned with a systematic spectrophotometric study of the stability of polyhalides of various organic (heterocyclic, quaternary ammonium, and phosphorus and sulfurcontaining)


cations and bisammonium dications by measuring an equilibrium shift in the system organic halide—iodine. For the first time, the stability constants of the resulting polyhalide β = [CtXI2]/([CtX][I2])

have been calculated from the function of the average iodine number n–I (the number of elemental iodine mol ecules coordinated by a molecule of a halide of an organic cation) n–I2 = (CI2 – [I2])/CCtX

by the formula lg[n n–I2/(1 – n–I2)] = lg[I2] + lgβ.

It has been found that the stability of complex iodine halides increases in the order I2Cl– < I2Br– < I3]; e.g., the logβ values of the corresponding acetylcholinium salts are 3.91, 4.39, and 5.35 (see Ref. 9). The same trend holds for the increasing size of the substituent at the quaternary N atom in fused heteroaromatic cations. For instance, the dependence of the stability constants of Nalkyl quinolinium triiodides on the alkyl chain length in the substituent shows a maximum for Nisopropylquinolinium triiodide (logβ = 6.60).93 The presence of electrondonat ing substituents in the organic cation, especially near the quaternary N atom, decreases the stability of iodine halides. For instance, carbacholinium diiodine chloride (logβ = 3.09) is less stable than acetylcholinium diiodine chloride (logβ = 3.91)9 and 1amino2(4chlorobenzyl) isoquinolinium diiodine bromide (logβ = 3.50) is less stable than 2propylisoquinolinium diiodine bromide (logβ = 4.34).85 The highly symmetrical tetraphenyl phosphonium cation makes the corresponding diiodine bromide very stable (logβ = 5.44), which is comparable in stability with triiodides of nitrogencontaining cations.90 The lowered stability of trimethylsulfonium triiodide (logβ = 4.63) is attributed to the small size of the coordi nating cation.94 Iodides of doubly charged organic cations such as bis[2(N,N,Ntrimethylammonio)ethyl] succinate and pxylylenebis(tetrahydrothiophenium) can simultaneously add two iodine molecules in solution to give very stable complexes. The stability constants of the former (logβ1 = 4.07, logβ2 = 8.86) and latter polyiodine iodides (logβ1 = 4.69, logβ2 = 8.59) have been estimated by the equation relat ing the function of the average iodine number n–I2 to the equilibrium concentration of iodine [I2] n–I2/{(1 – n–I2)•[I2]} = = β1 + β2[(2 – n–I2)/(1 – n–I2)]•[I2].

Using 1H NMR spectroscopy, one can study com plexation between organic halides and elemental iodine.53,87

1780


For instance, tri and pentaiodides as opposed to iodide are characterized by delocalization of the negative charge and a weaker polarizing effect of the anion on the cation. Because of this, the cationic protons in the organic iodine halide become more strongly shielded, especially for heteroaromatic fused cations. As the result, the signals for their protons are shifted upfield: e.g., the chemical shifts of the signal for the coordinated C(2)H proton of the imidazole ring differ by 1.6 ppm for 1,3diethylbenz imidazolium iodide and the corresponding triiodide.53 Precise estimates of the thermodynamic stability of iodine halides of organic cations95 enable targeted syn thesis of drugs capable of releasing molecular iodine at a desired level. By analyzing the constants of complexation between some drugs and molecular iodine, one can pre dict their physiological activity.96 In the last decade, attention has been given to the influence of nonaqueous media on the formation of polyhalides. According to data on the thermodynamics of the formation of the triiodide ion in methanol, ethanol, and npropanol in the presence of various electrolytes,80 the stability of the triiodide ions increases when moving from lower to higher alcohols, regardless of the electro lyte nature. In the study of the photochemical decom position of the triiodide ion,97 it has been noted that replacement of methanol by butan2ol, which are both used as solvating solvents, lowers the probability of the release of iodine species from the complex. The theoreti cal98 and experimental data17 given in Table 1 provide convincing evidence for the strong influence of solvating media on the stability of triiodide ions. The thermodynamics of complexation between an io dine—iodide system and amylose in aqueous solutions has been studied by potentiometric titration at different temperatures. The constants obtained made it possible to compare the complexing efficiencies of biomolecules.99,100 Combined experimental and theoretical investiga tions9,92,101,102 (Xray diffraction, optical spectroscopy, and quantum chemical calculations) of the structures of organic iodine halides are of great interest. Determination of the molecular structures of organic iodine halides and the direction of the cationanionic coordination in the crystalline state, the study of the dis proportionation mechanism and kinetics in iodinecoor Table 1. Stability constants of the triiodide anions in different solvents17 Solvent

lgK

H2 O MeOH EtOH PrnOH BunOH

2.87 4.17—4.30 4.65 4.76 6.0

Solvent Diethylene glycol MeCN DMSO DMF CHCl3

lgK 6.53 7.4 5.6 7.1 6.5


dinating solvents,19,20,36 and estimation of the thermo dynamic stability can be useful for the prediction of the pharmacological activity of drugs in various media, because the degrees of the release and disproportionation of molecular iodine depend on the solvent nature. A number of model compounds based on πconju gated (linear polymethine or cyclic aromatic) cations have been calculated using ab initio quantum chemical meth ods (RHF, MP2(full), and MP4(fc) in the basis sets HW+(3d), 321G+(d), and 631G++(d,p)). 15 It has been demonstrated that the anion differently coordinates acyclic conjugated and cyclic aromatic cations and is much more stable in the complexes with the latter. The spatial coordination of an iodine halide anion by an organic cation depends on its size, symmetry, and tendency toward hydrogen bonding. In the series of quaternary phosphonium compounds, 3carboxypropyl (triphenyl)phosphonium diiodine bromide shows the elec trostatic cation—anion interaction (unambiguous coor dination of the anion through the Br atom to the 3car boxypropyl(triphenyl)phosphonium cation),103 while an alternative coordination is found in tetraphenylphos phonium diiodine bromide (through the terminal atoms of the anion).90 Apparently, this is because the cation PPh4+ is a poor partner in hydrogen bonding.104 The formation of structures with equiprobable coordination of the diiodine bromide ion by the Npropylisoquinolinium cation through the terminal halogen atoms has been confirmed by Xray diffraction data.85 An interesting transformation has been noted in the recrystallization of the salt AsPh 4I2Br as a result of the disproportionation of the anion under the action of the solvent 2 CtBrI2 + Solv = CtBr2I(Solv) + CtI3(Solv).

According to Xray diffraction data, the crystal shows a superposition of the anions I3– and IBr2– (0.526/0.474) because of the interaction of the cation—anion couple (Ph4As+)(I3–/IBr2–).105 The shortest interionic distance is found between the H(4) atom of the phenyl ring and the central iodine atom of the anions (Fig. 7). The formation of such a hydrogen bond between the central atom of the triiodide ion and the H(6) atom of the pyridine ring has been detected in the crystal structure of di(pyridin2yl) disulfide triiodide, a product of oxidation of 2mercapto pyridine with molecular iodine.106 Despite a wealth of data on the compositions and structures of polyhalides of organic cations 107—109 and molecular iodine complexes,8 their crystallographic examination remains very intensive. For instance, the crystal and molecular structures of Ncetylpyridinium interhalides, 54 Npropylisoquinolinium diiodine bro mide, 85 Nmethyl(ethyl)quinolinium triiodides, 37,54 N,Ndiethylbenzimidazolium triiodide, 110 3carboxy



C(1A) C(7A) H(2A) H(12A) C(2) H(3A) Br(2a)/ C(12) As(1) I(2A) C(11) C(7) C(1) C(3) H(11A) H(8A) C(6) C(4) C(10) C(8) I(1) C(9) H(6A) C(5) H(4A) H(10A) H(9A) H(5A)

Iodine sorption by anionexchange resins is the most attractive method because of its sufficient selectivity and suitability at low temperatures.112 In this case, ion exchange does not occur; instead, a halogen molecule adds to the own ions of the ionexchange resin to give complex ions (iodine halides) retained more firmly than the initial ions. Anionexchange resins absorb well iodine from the gas phase and thus are used to trap radioactive iodine wastes from the exhaust gas of nuclear power stations.111 The anionexchange resins AB17x8, AB27, and AMP are in most common commercial use.111 Their respective structural formulas are shown below.

Br(2)/I(2) Fig. 7. General view of the cation—anion couple (Ph4As+)(I3–/ IBr2–) in the crystal with atomic thermal displacement ellipsoids (p = 50%).105

propyl(triphenyl)phosphonium diiodine bromide,103 tetra phenylphosphonium diiodine bromide,90 and pxylylene bis(tetrahydrothiophenium) triiodide91 have been deter mined in recent years. It follows from the data presented above that the mo lecular formula, size, shape, and stability of the polyiodine halide ion and the way of its coordination by an outer sphere organic cation depend on the nature and symme try of the cationic environment, the ability of a solvating solvent to form complexes with iodine, and the conditions of the synthesis. The crystal field substantially influences the geometry, the bond order, and the charge distribution in anions. Anions are more stable when the crystal lattice contains large cations favoring bond anisotropy and an alternative coordination of an interhalide ion (e.g., I2Br–) through its terminal halogen atoms. Apparently, the polyiodine iodide anions under discussion can be catego rized among stereochemically flexible structures.14 Practical applications of iodine halide systems Selective extraction of molecular iodine from natural sources is an important usage of iodine halides of organic cations. Halides of nitrogencontaining organic bases easily combine with iodine to form complex polyhalides bearing more than one iodine molecule per ion halide. Some quaternary ammonium halides, which themselves are well soluble in water, add iodine to give waterin soluble complex polyhalides. An example is trimethyl (myricyl)ammonium chloride capable of adding up to six iodine molecules.17 This salt, as well as some structural analogs, has been proposed for use in the extraction of iodine from natural brines.111 In this context, compounds with the N atom in the pyridine (cetylpyridinium chlo ride) or morpholine heterocycle are promising.

The scope of practical applications of polyiodide sys tems as conductors, magnetic materials, guest—host com plexes, electrolytes for solar cells,113,114 and biologically active compounds is unprecedentedly wide. Some foreign researchers discuss interphase electron transfer during the conversion of light energy in the presence of the electro lyte 3ethyl1methylimidazolium triiodide as a sensi tizer.115,116 Polyiodides are tested as components117 in the production of organic polymers with controllable electric properties.31,32 Compounds with active iodine are used as drugs and antimicrobial agents,64,65 in analytical chemistry,3,118,119 and for separation and purification purposes.120 References 1. H. Kusama, H. Arakawa, H. Sugihara, J. Photochem. Photobiol. A, 2005, 171, 197. 2. B. O´Reganoulos, M. Gratzel, Nature, 1991, 353, 737. 3. M. Ryouta, U. Nobuo, Anal. Biochem., 2004, 331, 169. 4. M. D. Mashkovskii, Lekarstvennye sredstva [Drugs], Torsing, Khar´kov, 1998, 2, 592 pp. (in Russian). 5. N. U. Aliev, L. P. Mamonova, N. A. Utarbaeva, Izv. Vuz., Khim. Khim. Tekhnol., 2003, 46, 77 [Bull. High Schools, Chem. Chem. Technol. (Engl. Transl.), 2003, 46]. 6. H. Shirakawa, E. J. Louis, A. G. McDiarmid, C. K. Chiang, A. J. Heeger, J. Chem. Soc., Chem. Commun., 1977, 579. 7. A. J. Heeger, Angew. Chem., Int. Ed. (Engl.), 2001, 40, 2591. 8. C. Nather, M. Bolte, Phosphorus, Sulfur, Silicon, Relat. Elem., 2003, 178, 453.

1782


9. S. S. Simonyan, Ph.D. (Chem.) Thesis, Rostov. Gos. Univ., RostovonDon, 2004, 166 pp. (in Russian). 10. V. T. Calabrese, A. Khan, J. Phys. Chem. A, 2000, 104, 1287. 11. M. C. Aragoni, M. Arca, F. A. Devillanova, A. Garau, F. Isaia, V. Lippolis, G. Verani, Coord. Chem. Rev., 1999, 184, 271. 12. J.F. Lagorce, A.C. JambutAbsil, J. Buxeraud, C. Moesch, C. Raby, Chem. Pharm. Bull., 1990, 38, 2172. 13. G. A. Landrum, N. Goldberg, R. J. Hoffman, J. Chem. Soc., Dalton Trans., 1997, 3605. 14. B. D. Stepin, S. B. Stepina, Usp. Khim., 1986, 55, 1434 [Russ. Chem. Rev. (Engl. Transl.), 1986, 55, 812]. 15. S. S. Simonyan, M. S. Chernovýants, M. E. Kletskii, Zh. Fiz. Khim., 2003, 77, 866 [Russ. J. Phys. Chem. (Engl. Trans.), 2003, 77, 774]. 16. S. S. Simonyan, M. E. Kletskii, M. S. Chernovýants, V. E. Goléva, Zh. Obshch. Khim., 2003, 73, 609 [Russ. J. Gen. Chem. (Engl. Transl.), 2002, 72, 575]. 17. Biologicheski aktivnye veshchestva v rastvorakh. Struktura, termodinamika i reaktsionnaya sposobnost´ [Biologically Active Compounds in Solutions. Structures, Thermodynamics, and Reactivities], Ed. A. M. Kutepov, Nauka, Moscow, 2001, 408 pp. (in Russian). 18. L. J. Andrews, R. M. Keefer, Molecular Complexes in Organic Chemistry, HoldenDay, San Francisco, 1964. 19. S. S. Simonyan, M. S. Chernovýants, E. O. Lykova, Zh. Fiz. Khim., 2005, 79, 1814 [Russ. J. Phys. Chem. (Engl. Transl.), 2005, 79, 1610]. 20. M. S. Chernovýants, S. S. Simonyan, E. O. Lykova, Izv. Akad. Nauk, Ser. Khim., 2003, 1801 [Russ. Chem. Bull., Int. Ed., 2003, 52, 1900]. 21. E. B. Podgornaya, M. S. Chernovýants, I. N. Shcherbakov, A. I. Pyshchev, Zh. Obshch. Khim., 1999, 69, 109 [Russ. J. Gen. Chem. (Engl. Transl.), 1999, 69, 105]. 22. F. C. Grozema, R. W. J. Zijlstra, M. Swart, P. Th. van Duijnen, Int. J. Quant. Chem., 1999, 75, 709. 23. J. T. Su, A. H. Zewail, J. Phys. Chem. A, 1998, 102, 4082. 24. P. S. Engel, S. Duan, K. H. Whitmire, J. Org. Chem., 1998, 63, 5666. 25. R. B. Walsh, C. W. Padgett, P. Metrangolo, G. Resnati, T. W. Hanks, W. T. Pennington, Cryst. Growth Design, 2001, 1, 165. 26. E. L. Rimmer, R. D. Bailey, W. T. Pennington, T. W. Hanks, J. Chem. Soc., Perkin Trans. 2, 1998, 2557. 27. F. Comby, A. C. JambutAbsil, J. Buxeraud, C. Raby, Chem. Pharm. Bull., 1989, 37, 151. 28. M. Esseffar, W. Bouab, A. Lamsabhi, J.L. M. Abboud, R. Notario, M. Yanez, J. Am. Chem. Soc., 2000, 122, 2300. 29. V. Daga, S. K. Hadjikakou, N. Hadjiliadis, M. Kubicki, J. H. Z. dos Santos, I. S. Butler, Eur. J. Inorg. Chem., 2002, 1718. 30. C. D. Antoniadis, S. K. Hadjikakou, N. Hadjiliadis, M. Kubicki, I. S. Butler, Eur. J. Inorg. Chem., 2004, 4324. 31. E. E. Laukhina, L. I. Buravov, E. B. Yagubskii, B. Zh. Narymbetov, L. V. Zorina, S. S. Khasanov, R. P. Shibaeva, N. V. Avramenko, K. Van, L. P. Rozenberg, Synth. Met., 1997, 90, 101. 32. A. Graja, R. S´wietlik, M. Potomska, A. Brau, J.P. Farges, Synth. Met., 2002, 125, 319. 33. P. Deplano, J. R. Ferraro, M. L. Mercuri, E. F. Trogu, Coord. Chem. Rev., 1999, 188, 71.


34. I. P. Romm, Yu. G. Noskov, A. A. Mal´kov, Izv. Akad. Nauk, Ser. Khim., 2007, 1869 [Russ. Chem. Bull., Int. Ed., 2007, 56, 1935]. 35. P. H. Svensson, L. Kloo, Chem. Rev., 2003, 103, 1649. 36. S. S. Simonyan, M. S. Chernovýants, Zh. Fiz. Khim., 2005, 79, 2014 [Russ. J. Phys. Chem. (Engl. Transl.), 2005, 79, 1791]. 37. O. N. Kazheva, G. G. Aleksandrov, O. A. Dýachenko, M. S. Chernovýants, E. O. Lykova, I. E. Tolpygin, I. M. Raskita, Koord. Khim., 2004, 30, 636 [Russ. J. Coord. Chem. (Engl. Transl.), 2004, 30, 599]. 38. Cambridge Structural Database System, Version 5.29, 2008. 39. J. H. Perlstein, Angew. Chem., Sect. B, 1977, 89, 534. 40. T. Handa, T. Yajima, Biopolymers, 1980, 19, 1723. 41. F. H. Herbstein, M. Kaftory, M. Kapon, W. Saenger, Z. Kristallogr., Teil B, 1981, 154, 11. 42. I. Pantenburg, K.F. Tebbe, Z. Naturforsch., Teil B, 2001, 56, 271. 43. R. Poli, J. C. Gordon, R. K. Khanna, P. E. Fanwick, Inorg. Chem., 1992, 31, 3165. 44. M. R. Bryce, A. K. Lay, A. Chesney, A. S. Batsanov, J. A. K. Howard, U. Buser, F. Gerson, P. Merstetter, J. Chem. Soc., Perkin Trans. 2, 1999, 755. 45. A. S. Gaballa, S. M. Teleb, E. Rusanov, D. Steinborn, Inorg. Chim. Acta, 2004, 357, 4144. 46. A. J. Blake, R. O. Gould, W. S. Li, V. Lippolis, S. Parsons, C. Radek, M. Schröder, Angew. Chem., Int. Ed. (Engl.), 1998, 37. 47. K.F. Tebbe, R. Loukili, Z. Anorg. Allg. Chem., 1998, 624, 1175. 48. A. J. Blake, V. Lippolis, S. Parsons, M. Schröder, Chem. Commun., 1996, 2207. 49. S. Lee, B. Chen, D. C. Fredrickson, F. J. DiSalvo, E. Lobkovsky, J. A. Adams, Chem. Mater., 2003, 15, 1420. 50. J. Ropponen, M. Lahtinen, S. Busi, M. Nissinen, E. Kolehmainen, K. Rissanen, New J. Chem., 2004, 28, 1426. 51. M. K. Nazeeruddin, P. Péchy, T. Renouard, S. M. Zakeeruddin, R. HumphryBaker, P. Comte, P. Liska, L. Cevey, E. Costa, V. Shklover, L. Spiccia, G. B. Deacon, C. A. Bignozzi, M. Grätzel, J. Am. Chem. Soc., 2001, 123, 1613. 52. H. Stegemann, A. Rohde, A. Reiche, A. Schnittke, H. Füllbier, Electrochim. Acta, 1992, 37, 379. 53. E. B. Podgornaya, Ph.D. (Chem.) Thesis, Rostov. Gos. Univ., RostovonDon, 1999, 169 pp. (in Russian). 54. G. V. Shilov, O. N. Kazheva, O. A. Dýachenko, M. S. Chernovýants, S. S. Simonyan, V. E. Goléva, A. I. Pyshchev, Zh. Fiz. Khim., 2002, 76, 1436 [Russ. J. Phys. Chem. (Engl. Transl.), 2002, 76, 1295]. 55. V. Burtman, A. Teplitsky, A. Zelichenok, Tetrahedron Lett., 2000, 41, 5397. 56. O. N. Kazheva, G. V. Shilov, O. A. Dýachenko, M. S. Chernovýants, Yu. A. Kirsanova, E. O. Lykova, I. E. Tolpygin, Zh. Neorg. Khim., 2007, 52, 620 [Russ. J. Inorg. Chem. (Engl. Transl.), 2007, 52, 562]. 57. W. I. Cross, S. M. Godfrey, C. A. McAuliffe, R. G. Pritchard, J. M. Sheffield, G. M. Thompson, J. Chem. Soc., Dalton Trans., 1999, 2795. 58. B. Domercq, T. Devic, M. Fourmigué, P. AubanSenzier, E. Canadell, J. Mater. Chem., 2001, 11, 1570. 59. E. R. Gordon, R. B. Walsh, W. T. Pennington, T. W. Hanks, J. Chem. Crystallogr., 2003, 5—6, 285.


60. M. S. Chernovýants, I. V. Burykin, Yu. A. Kirsanova, I. E. Tolpygin, Zh. Neorg. Khim., 2007, 52, 1474 [Russ. J. Inorg. Chem. (Engl. Transl.), 2007, 52, 1378]. 61. Y.J. Cheng, Z.M. Wang, C.S. Liao, C.H. Yan, New J. Chem., 2002, 26, 1360. 62. M. Heritier, C. Pasquier, S. Ravy, P. Senzier, A. Moradpour, T. Giamarchi, Organic Superconductivity “20th Anniversary”, EDP Sciences, Les Ulis Cedex A, France, 2000. 63. F. D. Lewis, X. Liu, J. Liu, S. E. Miller, R. T. Hayes, M. R. Wasielewski, Nature, 2000, 406, 51. 64. M. V. Gavrilin, Khim.Farm. Zh., 2001, 35, 33 [Pharm. Chem. J. (Engl. Transl.), 2001, 35, 35]. 65. M. A. Atemnkeng, J. PlaizierVercammen, A. Schuermans, Int. J. Pharm., 2006, 317, 161. 66. T. L. Bluhm, P. Zugenmaier, Carbohydr. Res., 1981, 89, 1. 67. T. C. Vincent, A. Khan, J. Polym. Sci., Sect. A, 1999, 37, 2711. 68. T. Someno, T. Hoshizaki, K. Kozawa, T. Uchida, H. Hayashi, T. Sugano, M. Kinoshita, Bull. Chem. Soc. Jpn, 1991, 64, 921. 69. V. T. Calabrese, A. Khan, J. Polym. Sci., Sect. A, 1999, 37, 2711. 70. O. Yasushi, O. Takahashi, O. Kikuchi, J. Mol. Struct. (Teochem.), 1998, 424, 285. 71. O. Yasushi, O. Takahashi, O. Kikuchi, J. Mol. Struct. (Teochem.), 1998, 429, 187. 72. C. D. Antoniadis, G. J. Corban, S. K. Hadjikakou, N. Hadjiliadis, M. Kubicki, S. Warner, I. S. Butler, Eur. J. Inorg. Chem., 2003, 1635. 73. F. Demartin, P. Deplano, F. A. Devillanova, F. Isaia, V. Lippolis, G. Verani, Inorg. Chem., 1993, 32, 3694. 74. K. Y. Rajpure, C. H. Bhosale, Chem. Mater. Chem. Phys., 2000, 64, 70. 75. P. J. Stang, J. Org. Chem., 2003, 68, 2997. 76. I. Stefanic, K.D. Asmus, M. Bonifacic, Phys. Chem. Chem. Phys., 2005, 5, 2783. 77. P. J. Skrdla, N. R. Armstrong, S. S. Saavedra, Anal. Chim. Acta, 2002, 455, 9. 78. P. Hobza, Z. Havlas, Chem. Rev., 2000, 100, 4253. 79. C. J. Margulis, D. F. Coker, R. M. LyndenBell, Chem. Phys. Lett., 2001, 341, 557. 80. A. V. Vladimirov, A. V. Agafonov, J. Therm. Anal., 1998, 54, 297. 81. R. M. LyndenBell, R. Cosloff, S. Ruhman, D. Danovich, J. Vala, J. Chem. Phys., 1998, 109, 928. 82. T. Koslowski, P. Vohringer, Chem. Phys. Lett., 2001, 342, 141. 83. M. W. Schmidt, K. K. Balgridge, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. H. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. J. Su, T. L. Windus, M. Dupuis, J. A. Montgomery, J. Comput. Chem., 1993, 14, 1347. 84. M. S. Chernovýants, E. B. Podgornaya, A. I. Pyshchev, I. N. Shcherbakov, Zh. Obshch. Khim., 1998, 68, 822 [Russ. J. Gen. Chem. (Engl. Transl.), 1998, 68, 755]. 85. E. O. Lykova, M. S. Chernovýants, O. N. Kazheva, A. N. Chekhlov, O. A. Dýachenko, Zh. Fiz. Khim., 2004, 78, 2022 [Russ. J. Phys. Chem. (Engl. Transl.), 2004, 78, 1785]. 86. S. S. Simonyan, M. S. Chernovýants, M. E. Kletskii, A. I. Pyshchev, in Organicheskii sintez v novom stoletii (Tez. 3i Mezhdunarodnoi shkolykonferentsii po organicheskomu sintezu) [Organic Synthesis in the New Century (Abstrs, 3rd Int. SchoolConf. on Organic Synthesis)], St.Petersburg, 2002, 323 (in Russian).


87. V. E. Goléva, M. S. Chernovýants, A. I. Pyshchev, Zh. Fiz. Khim., 2001, 75, 1383 [Russ. J. Phys. Chem. (Engl. Transl.), 2001, 75, 1255]. 88. L. A. Bengtsson, A. Oskarsson, H. Stegemann, A. Redeker, Inorg. Chim. Acta, 1994, 215, 33. 89. K. Tashiro, M. K. T. Kawai, K. Yoshino, Polymer, 1997, 38, 2867. 90. O. N. Kazheva, A. A. Aleksandrov, O. A. Dýachenko, M. S. Chernovýants, S. S. Simonyan, E. O. Lykova, Koord. Khim., 2004, 30, 784 [Russ. J. Coord. Chem. (Engl. Transl.), 2004, 30, 739]. 91. I. V. Burykin, M. S. Chernovýants, N. V. Aleshina, Izv. Akad. Nauk, Ser. Khim., 2007, 1341 [Russ. Chem. Bull., Int. Ed., 2007, 1390]. 92. O. N. Kazheva, O. A Dýachenko, M. S. Chernovýants, V. E. Goléva, A. I. Pyshchev, Zh. Obshch. Khim., 2002, 72, 1613 [Russ. J. Gen. Chem. (Engl. Transl.), 2002, 72, 1521]. 93. E. O. Lykova, Ph.D. (Chem.) Thesis, Rostov. Gos. Univ., RostovonDon, 2006, 182 pp. (in Russian). 94. M. S. Chernovýants, I. V. Burykin, N. V. Aleshina, Zh. Anal. Khim., 2008, 63, 745 [Russ. J. Anal. Chem. (Engl. Transl.), 2008, 63, 680]. 95. M. S. Chernovýants, V. E. Goléva, E. O. Lykova, A. V. Faraponov, Izv. Vuz., Khim. Khim. Tekhnol., 2005, 48, 12 [Bull. High Schools, Chem. Chem. Technol. (Engl. Transl.), 2005, 48]. 96. M. N. Tsarevskaya, V. V. Sidorenko, T. A. Bityukova, Ukr. Khim. Zh. [Ukranian Journal of Chemistry], 1987, 53, 986 (in Russian). 97. E. Gershgoren, U. Banin, S. Ruhman, J. Phys. Chem. A, 1998, 102, 9. 98. H. Sato, F. Hirata, A. Myers, J. Phys. Chem. A, 1998, 102, 2065. 99. A. V. Vladimirov, T. V. Volkova, A. V. Agafonov, Zh. Fiz. Khim., 2003, 77, 690 [Russ. J. Phys. Chem. (Engl. Transl.), 2003, 77, 612]. 100. A. V. Agafonov, T. V. Volkova, A. V. Vladimirov, Zh. Fiz. Khim., 2003, 77, 1985 [Russ. J. Phys. Chem. (Engl. Transl.), 2003, 77, 1784]. 101. V. E. Goléva, Ph.D. (Chem.) Thesis, Rostov. Gos. Univ., RostovonDon, 2003, 184 pp. (in Russian). 102. M. S. Chernovýants, V. E. Goléva, A. I. Pyshchev, Zh. Anal. Khim., 2003, 58, 161 [Russ. J. Anal. Chem. (Engl. Transl.), 2003, 58, 139]. 103. O. N. Kazheva, A. A. Aleksandrov, O. A. Dýachenko, M. S. Chernovýants, S. S. Simonyan, E. O. Lykova, Koord. Khim., 2003, 29, 883 [Russ. J. Coord. Chem. (Engl. Transl.), 2003, 29, 819]. 104. R. Minkwitz, M. Berkei, Z. Naturforsch., Teil B, 2001, 56, 39. 105. M. S. Chernovýants, I. V. Burykin, N. V. Aleshina, Zh. Obshch. Khim., 2008, 78, 1109 [Russ. J. Gen. Chem. (Engl. Transl.), 2008, 78, 1345]. 106. C. D. Antoniadis, S. K. Hadjikakou, N. Hadjiliadis, M. Kubicki, I. S. Butler, Eur. J. Inorg. Chem., 2004, 4324. 107. J. D. Dunitz, J. Bernstein, Acc. Chem. Res., 1995, 28, 193. 108. J. Bernstein, R. J. Davey, J. O. Henck, Angew. Chem., Int. Ed., 1999, 38, 3441. 109. A. L. Bingham, D. S. Hughes, M. B. Hursthouse, R. W. Lancaster, S. Tavener, T. L. Threlfall, Chem. Commun., 2001, 603.

1784


110. V. V. Gritsenko, O. A. Dýachenko, M. S. Chernovýants, E. B. Podgornaya, A. I. Pyshchev, Zh. Obshch. Khim., 1999, 69, 142 [Russ. J. Gen. Chem. (Engl. Transl.), 1999, 69, 138]. 111. V. I. Ksenzenko, D. S. Stasinevich, Khimiya i tekhnologiya broma, ioda i ikh soedinenii [The Chemistry and Technology of Bromine, Iodine, and Their Compounds], Khimiya, Moscow, 1995, 432 pp. (in Russian). 112. T. D. Panasenko, V. V. Sokolov, Proizvodstvo ioda iono obmennym metodom [Production of Iodine by IonExchange Methods], NIITEKhim, Moscow, 1986, 181 pp. (in Russian). 113. H. Kusama, H. Arakawa, H. Sugihara, J. Photochem. Photobiol. A, 2005, 171, 197. 114. S. Chengwu, D. Songyuan, W. Kongjia, P. Xu, G. Li, Z. Longyue, H. Linhua, K. Fantai, Sol. Energy Mater. Sol. Cells, 2005, 86, 527.


115. 116. 117. 118.

A. Hagfeldt, M. Graetzel, Chem. Rev., 1995, 95, 49. R. Kawano, M. Watanabe, Chem. Commun., 2003, 330. H. K. AbdelAal, Int. J. Hydrogen Energy, 1984, 9, 767. J. A. Ortuno, C. SanchezPedreno, J. Hernandez, D. J. Oliva, Talanta, 2005, 65, 1190. 119. B. Saad, W. T. Wai, B. P. Lim, M. I. Saleh, Anal. Chim. Acta, 2006, 565, 261. 120. V. E. Plyushchev, B. D. Stepin, Analiticheskaya khimiya rubidiya i tseziya [The Analytical Chemistry of Rubidium and Cesium], Nauka, Moscow, 1975, 224 pp. (in Russian).

Received April 4, 2008; in revised form November 6, 2008